This invention relates to the field of fluid filters and in particular to new and improved flow line filters.
The placing of fluid filters in flow line fittings is known. Early examples are disclosed in U.S. Pat. Nos. 249,172; 292,912; 417,399; 295,926; 1,063,467; and 2,779,478. These filters were improved by providing access to the filter element for enabling replacement without the need to remove the filter housing from the flow path. For examples, see U.S. Pat. Nos. 1,152,831; 1,682,655; 1,917,203; and 2,545,789.
A limiting factor in the use of flow line filters as strainers has been the fluid pressure drop and inherently related flow rate through such filters. Some attempts to overcome that problem include U.S. Pat. Nos. 398,735; 664,280; 852,584; 1,213,140; 2,011,031; 2,028,520; 2,260,874; 2,369,740; 2,820,702; and 3,481,474. In general, these prior art solutions employed an enlarged flow housing having inlet and outlet openings that did not conform to the standardized dimension of pipe fitting as established by the American Standards Association (ASA) and now universally accepted. Another solution such as disclosed in U.S. Pat. No. 983,352 and 2,979,209, has been to reinforce the filter screen to withstand the greater differential pressure resulting from high capacity flow.
Removing the filtered sediment from the flow housing has also presented some problems. One means for overcoming such problem is disclosed in U.S. Pat. No. 2,372,445, while U.S. Pat. Nos. 555,685 and 1,704,634 represent earlier attempts to overcome that same problem. Self-cleaning filter screens, such as disclosed in U.S. Pat. No. 3,487,931, have also been employed. Backwash means, such as disclosed in U.S. Pat. Nos. 3,387,712; 3,828,930 and mechanical means, such as disclosed in U.S. Pat. No. 2,022,017, have also been employed to prevent clogging of the filter and attendant increases in pressure drop and decreases in flow capacity.
Often inline flow filters were combined in a standard dimension flow housing with a valve which further reduced the filter flow capacity. Examples of such filters are disclosed in U.S. Pat. Nos. 2,017,350 and 3,735,874.
An improved flow line filter having fine screening capability coupled with high capacity has been commercially available from the assignee of the present invention under the trademark "CORE-T." In general, these fluid filters provide a filter housing having standard pipe dimensions and employed a self-cleaning filter screen employing a helically wedge wire filter element that provides means for back-flushing. Such filter elements are generally of the type disclosed in U.S. Pat. Nos. 3,561,605; 3,584,685; and 3,667,615. Such filters have been custom fabricated rather than mass produced as the filter screens were not interchangeable between filter housings due to variations in filter length. Both straight through and 90.degree. elbow designs have been custom manufactured.
U.S. Pat. No. 3,011,644 to Farrell, et al. discloses a flow line filter screen in which the filter screen is easily accessible to enable rapid changing. The interchangeable filter screen is held in position by a bow spring in both disclosed embociments. In the straight through flow embodiment, the lug 35 serves to limit longitudinal movement of the screen, but the build up of a sufficient pressure differential across the screen will result in overcoming the urging of the bow spring and tilting of the filter element which breaks the seal and effectively by-passes the fluid about the filter element. In the 90.degree. elbow embodiment, the pressure differential also will overcome the urging of bow spring 69 to break the seal and enable the undesired by-pass flow.
U.S. Pat. No. 1,223,299 discloses a filter that is positively held against inadvertent by-pass leakage due to pressure build up across the filter, but the filter screen extended beyond the standard dimension between the inlet and outlet of a pipe fitting. Such an arrangement is also disclosed in U.S. Pat. No. 2,507,591.